The invention relates to a closure cap with the features of the preamble of patent claim 1.
Closure caps of plastic material are applied in multitude for closing containers, for example drinks bottles.
In particular with carbon-dioxide containing drinks, but also with fruit juices, there exists the problem that the inner pressure in the container in the course of time may rise (by temperature increase or fermentation). Since closure caps usually should seal as good as possible in order to prevent leakages there exists the danger that the container on account of an increased inner pressure explodes. Above all with glass bottles exploding glass fragments represent a potential danger.
For solving this problem already various types of closure caps have been suggested.
From EP 597 867 it is for example known to provide a closure cap with a sealing inlay and simultaneously to define the screw on position of the closure cap. With an increased inner pressure the sealing disk is to be compressed, and with this act as a safety valve.
From EP 464 384 there is known a self-bleeding bottle closure with which by way of fluctuations in the head plate the sealing effect at an increased inner pressure is lifted.
From DE 196 13 830 there is known a self-bleeding closure in which the cap base is weakened. The weakening leads to the fact that with an increased inner pressure the cap base is curved outwards (so-called doming) and that with this an inner sealing formed as one piece with the cap base is relieved of pressure.
All these known solutions however have certain disadvantages. The degree of compression of an inlayed sealing disk can only be controlled with great difficulty. Furthermore the pressing of the sealing disk over the whole circumference of the container opening is homogeneous so that the exact control of the bleeding procedure is difficult.
With closure caps provided with weakenings in the head plate there exists the problem that an inner sealing, on account of the doming, is relieved of pressure, but that seals which seal at the upper opening edge and above all outside on the container opening, by way of this are not relieved of pressure.
It is the object of the invention to avoid the disadvantages of the known, in particular thus to provide a closure cap which with an optimal sealing under normal conditions permits a reliable and exactly controllable bleeding with an increased inner pressure in the container closed by the closure cap. The closure cap is to be simply and economically manufacturable and able to be screwed on with usual screw-on devices.
According to the invention these objects are achieved by a closure cap with the features of the characterising part of patent claim 1.
The closure cap consists essentially of a cap base and a cap wall. On the cap base there is provided an inner seal. The seal is provided with a seal line which can be pressed against the inner side of the container opening and with this achieves a sealing effect.
The closure cap may be retained on the container opening by retaining elements arranged on the inner side of the cap wall, for example by a screw thread.
The closure cap comprises a first abutment which rises roughly from the base.
According to the invention axially between the retaining elements and the first abutment there is arranged a second abutment for limiting the screwing-on movement of the closure cap. The second abutment may for example come into engagement with the beginning of a thread on the container opening and thus limit the screwing-on movement. The second abutment is advantageously formed as a circumferential ring whose abutment plane runs roughly perpendicular to the axis of the closure cap.
The cap wall is furthermore provided with a deformable wall section. The deformable wall section is arranged between the first and the second abutment. The deformability may be achieved by a weakening of the wall thickness in the region of the wall section, for example by way of a deepening on the inner side of the cap wall.
The inventors of the present invention have ascertained that a weakening of the closure cap in the region of the cap wall in contrast to known weakenings in the cap base has surprising advantages. An increased inner pressure in the container closed by the closure cap does not lead in the first case to a curving of the cap base, but to an axial displacement of the cap base. The movement is thus essentially linear. This means that any seals on the outer side or on the end-face side of the container opening on account of the axial translation movement of the cap base likewise come out of sealing engagement. Of course as previously a certain curvature may occur.
So that the closure cap bleeds at the correct point in time on the one hand the axial distance between the first and the second abutment, and on the other hand the penetration depth of the sealing line are selected in a manner such that the sealing line given a predetermined inner pressure comes out of engagement with the inner side of the container opening. This minimal pressure is different according to the material filled in the container. With fruit juices it is at about 2 bar, with low CO2-containing drinks at 5 bar and with a content with 4 Vol. % CO2 above 8 bar. The degree of deformability of the wall section is likewise correspondingly selected.
The first abutment on screwing-on comes into engagement with the upper side of the container opening before the second abutment comes into engagement with the beginning of the thread.
Therebetween the first abutment and the deformable wall region are deformed on account of the screwing-on movement.
The penetration depth of the sealing line defines the axial distance of the sealing line from the first abutment in the deformed condition or the distance of the sealing line to the upper side of the container opening.
By way of the directed choice of the distance between the abutments and the deformability of the wall section, the deformable wall section on screwing on the closure is pretensioned to a predetermined value in the manner of a spring.
By way of a suitable choice of the penetration depth of the sealing line the point in time of the bleeding may be predetermined. If the inner pressure is so large that the cap base is displaced against spring force by the penetration depth the closure bleeds.
The deformability is set for normal conditions, i.e. for temperatures in the region of 15-35xc2x0. If the outer temperature exceeds these values, the deformability becomes larger (softening of the plastic material). The bleeding function is therefore favoured at a higher temperature.
The two abutments serve the exact defined pretensioning of the weakening zone in the cap wall. With this an exactly predefined bleeding pressure may be set.
The inner seal comprises also advantageously bleeding reliefs on its side facing the cap skirt. The sealing reliefs are arranged below the sealing line. The inner seal is advantageously formed as a so-called olive seal. This means that the sealing line defines a maximum outer diameter of the inner seal and is arranged distanced to the inner side of the cap base. Such olive seals have the advantage of sealing in the inside of the container opening where normally there is to be found an exactly defined sealing surface without damage. The disadvantage of such olive seals is however that on acount of the pretensioning they already seal when the closure cap is not located in the placed-on condition, but axially slightly above the sealing position. Thanks to the bleeding reliefs which advantageously begin directly below the sealing line the sealing effect is lifted as soon as the sealing line lies outside of the container opening. An extension of the sealing effect on account of, the displacement of the sealing line over the inner seal which tapers conically downwards is thus prevented.
The closure cap may furthermore be provided with a circumferential sealing bulge which can be pressed against the outer side of the container opening. The sealing bulge is axially arranged between the first and second abutment.
The closure cap is furthermore advantageously provided with retaining-open elements. Such retaining-open elements may for example be provided above the sealing line on the surface of the inner seal, which faces the cap wall. The retaining-open elements prevent a displacement of the sealing line. If with an increased inner pressure is should however come to a doming of the cap base, the retaining-open elements are supported on the container opening so that the position of the inner seal with respect to the container opening is essentially only changed by translation. Retaining-open elements may of course also be provided on the remaining sealing elements, in particular on the second abutment acting as a seal or on the optional annular bulge pressing against the outer side of the container.